1. Field of the Invention
The present invention pertains to laser detection and ranging (“LADAR”) systems and, more particular, to a LADAR system employer a fiber laser light source.
2. Description of the Related Art
A need of great importance in military and some civilian operations is the ability to quickly detect and identify objects, frequently referred to as “targets,” in a “field of view.” Techniques for identifying targets have existed for many years in military contexts. For instance, in World War II, the British developed and utilized radio detection and ranging (“RADAR”) systems for identifying the incoming planes of the German Luftwaffe. RADAR uses radio waves to locate objects at great distances even in bad weather or in total darkness. Sound navigation and ranging (“SONAR”) has found similar utility and application in environments where signals propagate through water, as opposed to the atmosphere. While RADAR and SONAR have proven quite effective in many areas, they are inherently limited by a number of factors. For instance, RADAR is limited by its use of radio frequency signals and the size of the resultant antennas used to transmit and receive such signals. Sonar suffers similar types of limitations.
The art consequently developed and deployed a variety of alternative technologies. One such alternative technology is laser detection and ranging (“LADAR”). Similar to RADAR systems, which transmit radio waves and receive radio waves reflected from objects, LADAR systems transmit laser beams and receive reflections from targets. Because of the short wavelengths associated with laser beam transmissions, LADAR data exhibits much greater spatial resolution than RADAR data. LADAR systems are therefore useful in many applications for locating and identifying objects including, in military environments, automatic target recognition (“ATR”) systems. However, LADAR's versatility has led to its application in a variety of contexts. For instance, LADAR systems are sometimes used in navigation as range finders, etc.
A number of LADAR systems have been developed. Of significant importance to LADAR systems is the hardware that transmits the laser beam and the hardware that receives the reflected signals. Frequently, this hardware is combined into a single “transceiver.” Exemplary LADAR transceiver technology is disclosed in the following U.S. patents:                U.S. Letters Patent 4,085,910, entitled “Dual Mode Optical Seeker for Guided Missile Control”, issued Apr. 25, 1978, to Northrop Corporation as assignee of the inventor(s) William G. Baker, et al.;        U.S. Letters Patent 4,515,471, entitled “Scanning Laser Radar”, issued May 7, 1985, to LTV Aerospace and Defense Company as assignee of the inventor(s) Dayton D. Eden;        U.S. Letters Patent 4,515,472, entitled “Agile Receiver for a Scanning Laser Radar”, issued May 7, 1985, to LTV Aerospace and Defense Co. as assignee of the inventor(s) Albert B. Welch;        U.S. Letters Patent 4,528,525, entitled “Scanning Laser for a Scanning Laser Radar”, issued Jul. 9, 1985, to LTV Aerospace and Defense as assignee of the inventor(s) Dayton D. Eden, et al.;        U.S. Letters Patent 5,200,606, entitled “Laser Radar Scanning System”, issued Apr. 6, 1993, to LTV Missiles and Electronics Group as assignee of the inventor(s) Nicholas J. Krasutsky, et al.;        U.S. Letters Patent 5,224,109, entitled “Laser Radar Transceiver”, issued Jun. 29, 1993, to LTV Missiles and Electronics Group as assignee of the inventor(s) Nicholas J. Krasutsky, et al.;        U.S. Letters Patent 5,701,326, entitled “Laser Scanning System With Optical Transmit/Reflect Mirror Having Reduced Received Signal Loss”, issued Dec. 23, 1997, to Loral Vought Systems Corporation as assignee of the inventor(s) Edward Max Flowers; and        U.S. Letters Patent 6,262,800, entitled “Dual Mode Semi-Active Laser/Laser Radar Seeker”, issued Jul. 17, 2001, to Lockheed Martin Corporation as assignee of the inventor(s) Lewis G. Minor.The patents are listed in chronological order by date of issuance. Note that this list is exemplary only, and is not exhaustive.        
Most of these conventional LADAR transceivers employ a diode pumped solid state laser (“DPSSL”). The laser beam is manipulated by discrete optical components that require alignment and have unavoidable reflective losses. The transmitted and received signals are separated by a hole mirror or a polarizing beam splitter. The received signals are focused into an optical fiber and routed to electronic circuitry that captures and processes them.
However, performance requirements for LADAR systems continually demand higher performance. These requirements pressure current standards for signal handling efficiency and signal quality, as well as system cost, size and weight. Furthermore, ruggedization is becoming more important as LADAR systems are deployed in ever more difficult environments. This is particularly important in LADAR systems with respect to the alignment of the optics.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.